Question

I am having trouble with linked lists in C, I have only done data structures such as this in c++.

Gdb is giving me a

Program received signal SIGSEGV, Segmentation fault.
0x0804a23c in addArg (base=0x1, argument=0x804e410 "is") at myshell.c:42
42 while ( (curr != NULL) && (curr->n != NULL) )

I am familiar with segmentation faults having to do with memory, however I thought I have allocated memory correctly. What am I doing wrong?

addArg is being called as addArg(currentCmd->args, lexeme);and currentCmd is a pointer to a node struct

struct lnode {
 char *x;
 struct lnode *n;
};


struct node
  {
    char *command;
    struct lnode *args;
    int input;
    int output;
    int error;
    char *in;
    char *out;
    char *err;
    struct node *next;
    struct node *prev;
  };



void addArg(struct lnode *base, char *argument)
 {
 struct lnode *curr = base;

//this is line 42
  while ( (curr != NULL) && (curr->n != NULL) )
    curr = curr->n;

   curr -> n = malloc(sizeof(struct lnode));
   curr = curr->n;
   curr->x = strdup(argument);
   curr->n = NULL;
 }




struct node* createNode(char *command_, int input_, int output_, int error_, char *in_, char *out_, char *err_, struct node *prev_)
  {
  struct node *n;
  n = malloc(sizeof (struct node));
  n->command = strdup(command_);
  n->prev = prev_;
  n->next = NULL;
  n->input = input_;
  n->output = output_;
  n->error = error_;
  n->in = in_;
  n->out = out_;
  n->err = err_;
  n->args=malloc(sizeof(struct lnode));

 return n;
  }

Answer 1

I solved this issue by making the lnode *args into lnode args and making the required changes to memory managment.